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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | Ten-Tec Centaur Help

Reviews Summary for Ten-Tec Centaur
Ten-Tec Centaur Reviews: 31 Average rating: 4.8/5 MSRP: $749
Description: Full QSK 600W HF linear amplifier
Product is in production.
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KZ4B Rating: 5/5 Feb 7, 2016 00:24 Send this review to a friend
Very Robust Mid-power Amp  Time owned: more than 12 months
The Centaur Amplifier is functionally very desirable in it's output power range and physically attractive-- though relatively rare and no longer in production.

If relatively short duty cycle operation (i.e. SSB &/or CW) is the only need--then 811A Finals with 65 Watt Plate Dissipation (X 3 tubes) will suffice. There is zero power output improvement by upgrading to 572B Finals rated for 160 Watts Plate Dissipation (X 3 tubes). If more demanding/longer duty cycle (AM &/or RTTY) operation is needed then 572B's guarantee more reliable operation.

Note that only Svetlana Brand Tubes (Whether 811A,s or 572B's) have an Amplification Factor/Gain of 200--as opposed to 160 which is common with all other brands. Also, Svetlana's were engineered for the Centaur's horizontal (as opposed to vertical) tube orientation--which can be a problem with some other tube brands. The higher Amplification Factor/Gain of the Svetlana Tubes reduce the associated amplifier's relative Drive Power Requirement relative to amplifiers using all other brand tubes. This is especially important for the Centaur because it uses a less efficient "Swamping Resistor" in the Grid Circuit (as opposed to a "Tuned Circuit" used in most other amplifiers). Depending upon available Tranciever Output Power / Amplifier Drive Power (typically 100 Watts SSB/CW and 25 to 50 watts AM)--the Centaur is more likely to be Drive-Limited if using OTHER THAN Svetlana Tubes. Bottom line, try to use (OEM Ten-Tec supplied) Svetlana Tubes if possible and practical.

Note that the above-mentioned Swamping Resistor in the Centaur's Grid Circuit (while slightly increasing the Amplifier's relative Drive Requirement) helps eliminate the need for an often troublesome Neutralization Circuit and reduce Parasitic Oscillations. This inherent LACK of Feedback Oscillations/Instability (associated with Triode Amplifiers) contributes greatly to the reliability of the Centaur. Despite the improved stability, you are well advised to use about 20 or 25 feet of RG-58 Coax Cable between the Transceiver Output and Amplifier Input to further suppress VHF Range Parasitic Oscillations. This "trick" (which can be recommended for all Linear Amps) was originally recommended by Collins Radio for their 30L1 Amplifier which is a 4 tube version of the Centaur.

Many of the reviews herein mention the very troublesome Miniature "Bat-Handle" Toggle Switches which fail mechanically. They are a royal "pain" to replace--so when the first switch fails--change them all. The no-longer-available OEM Ten-Tec replacement switches are "crap". Radio Shack sells much higher quality switches : SPST (All-Metal Flat-Sided Bat Handle Mini- Toggle) 6A 120 V, 3A 240 V. Rad.Shack Stock # 275 635; DPDT (Same Specs As Above) Rad. Shack Stock # 275 636. Mouser and Newark Electronics may have something similar.

Ten-Tec no longer supports the Centaur--but maybe if/when they get back on their feet this will change.

If you get a Centaur that hasn't been modified for 10 Meter Operation--then there will be three small ferrite torroids on the small nominal 2 X 3 inch "Filter Board" located under the cover on the back of the Centaur (that accesses the 120/240 VAC Power Transformer Primary Circuit Jumper Board). If your Centaur HAS BEEN MODIFIED for 10 Meter Operation then there is only one small ferrite toroid on the SAME (same part number) board. The point is that the Ten-Tec Owner's Manual says you need a new board from Ten-Tec (which is no longer available)--but it is really the same board with two toroids removed. No other changes are thought to be needed to get on 10 Meters. Check with a licensed ham (including the writer) who has a 10 Meter capable Centaur to find out which Toroid should remain.

The Centaur's Power Transformer is very robust, so it doesn't thermally limit Plate Current, nor do the 572B Tubes whose Plates barely get red under maximum continuous loading. The Power transformer can be connected either for 120 or 240 VAC Utility Power Input--but there are no extra Buck/Boost Windings. While the Centaur is very happy being powered from 120 VAC, a 240 VAC supply is needed to maintain 1600 VDC under maximum loading. This yields 600 Watts+ PEP on SSB and a solid 500 Watts "key down". With 25 Watts Carrier Input you get 100 Watts carrier Output on AM. There is "headroom" for greater Amplifier Output with more Drive if available

The Centaur Fan is a bit noisy due to some over-kill in air flow. There are numerous ways to slow down or replace the fan as discussed elsewhere in this review. We noticed that most Fan Noise comes from the left-side Fan Inlet and not the Fan Outlet side. We built (out of 1/2" thick closed cell packing foam) a 5" X 5" X 5" Box open on two adjacent sides. One open side of the Box goes against the Fan Inlet Opening of the Centaur Enclosure and the other open side faces toward the rear of the amplifier. The noise reduction is remarkable with no decrease in cooling air flow.
VA2DV Rating: 5/5 Jun 21, 2015 07:59 Send this review to a friend
Good, solid and easy to tune  Time owned: 0 to 3 months
This is a wonderful amp. Built like a tank,
Have all the necessary metering. Tubes are robust and inexpensivea if you need to replace them.
COnstruction and finish way better than the competition with 3 811's.
And of cource, the legendary support from TT.
Rare on the market. If you see one, grab it !
K4AAZ Rating: 5/5 Sep 13, 2013 08:50 Send this review to a friend
great amp ,rarely seen for sale  Time owned: 3 to 6 months
Local ham had one for sale,pristine condition,he had sent it to Ten Tec for check up..I replaced 811 tubes with 572B ,replaced fan with quieter 40 to 50 watts from transceiver get 400 to 500 watts out on 110 ,tunes easy,nice small amp....
N1DZ Rating: 5/5 Nov 9, 2010 19:20 Send this review to a friend
Great amp  Time owned: more than 12 months
This is an update of a previous review. I am using this amp now for over 12 years. Modified the fan and made it nearly silent with a heavy duty serie resistor. Using 572b tubes. Recently recapped and added a Harbach soft start. Tuning is super smooth and output is 500-600 Watts. Recently I had a problem with a hanging input relais. Called Ten-Tec and within 5 days I had a replacement relais for less than $12.00. Mind you this amp has not been in production for many years. What a service!
This is a great 600 Watts amp, solidly built with great factory support. Unfortunately Ten-Tec does not make this amp anymore.
AF5U Rating: 5/5 Sep 18, 2010 08:26 Send this review to a friend
Modified - Now Almost Perfect  Time owned: more than 12 months
I bought this amplifier as a walk-in at the factory in 2001. It was preowned. Went through several final sets of tubes both 811As and 572Bs. Blew out components on the circuit boards. One day I found and solved the problems. Also did several modifications to solve the jump off the bench when you turn it on issue (current surge), the fan (120VAC) noise (now use 24VDC fan on 12VDC), and the LOAD capacitor plate shorting. Now the thing could not be sweeter. Love the QSK in CW and ruggedness of the 811As - don't waste your money on 572Bs. Yes, you "might" get a few more watts but at what cost per watt? Need a 100 bucks in your pocket - put in 811As! The guy you QSO will never till the difference on his s-meter.
AB3EN Rating: 5/5 Jul 16, 2010 03:40 Send this review to a friend
Great used buy!  Time owned: more than 12 months
I picked up this amp about 1 year ago. The previous owner had new 811's installed and one blew as I started it up. I replaced the 811's with 572B's and got new resistors for the plate connector board. I get a solid 700+ watts peak out of the amp with 75 watts drive, as indicated on the LP-100 wattmeter. It is a nice addition to my K3 and really helps in the morning with the rotten apples (7.238). If you can find one buy it, if run in to problems Ten Tec is there to help you. Both Ten Tec and Elecraft have the best customer service I have seen. Both make great products!
W4HT Rating: 5/5 May 1, 2010 15:00 Send this review to a friend
Top Quality Top Drawer Medium Power HF Amp  Time owned: more than 12 months
I have owned the Ten Tec Centaur now for about 3 years and it been flawless. No bangs, pops, or any anomalies. It is easy to tune and still produces 500 clean watts on CW and about 600 watts PEP on SSB. By the way, I am still using the original Svetlana 811A tubes that came with the amp from the factory. I only use the it in about a thrid of my QSO's but it's great when needed. I do agree with the comment regarding the wimpy switches. I haven't had to replace any of them yet but it does not appear that diffucult to get at them. All in all a quality medium power amp with inexpensive 811A tubes, a well written owners manual, and yes Ten Tec is still in business and will answer questions reagrding this product(or anytning else they have produced over the years). If you can find a good specimen buy it and enjoy!
W8UDX Rating: 5/5 Dec 21, 2009 18:53 Send this review to a friend
A great old friend  Time owned: more than 12 months
I was thinking tonight that every time one of my three very high-end amplifiers thumps and ceases to produce RF, I always take the cover off my Centaur, replace the big, non-functioning brute, and I am back up and running. I think that just about says it all. Thank you old friend.
WD9CMD Rating: 5/5 Apr 18, 2008 14:51 Send this review to a friend
Centaur is still perking along  Time owned: more than 12 months
After several years on the same set of chinese 572b tubes, I must commend the TT folks for a rock solid amp. The only issue with the amp is the wimpy switches. I've replaced one last year that went bad and then..... now the Ig/FWD is bad. Bummer. Why, because they are an absolute b.... to change out. Very hard to access, and way too small for what they do. Oh well, if thats the only thing wrong, so be it. It still works like a top. Quiet with the pabst fan and excellent out put with the 572b's. Also loads up great on 17m on the 15m bandswich. I can push this amp to 800w out on 40 most any time without excess heating apparent. I'd only try this on SSB (and not for ragchew) as if you did this on another mode, excess heating may fry some components. Anything more than say 650 out is a waste anyway. If you need more go to a bigger amp !! But I find this amp to be perfectually adequate for the majority of ham operating.
Good luck, David wd9cmd
NB7I Rating: 5/5 Apr 15, 2008 13:59 Send this review to a friend
Fine QSK Amp  Time owned: more than 12 months
I bought one years ago, and never had any trouble with it. It put out 600 watts with no trouble, but ran it at 500w. Not sure why there were so many who couldn't get that out of it. Using it with a QSK radio showed the big advantage over similiar amps.
I sold it only because I didn't need an amp anymore.
The high drive requirement may be due to the simple input circuit - a 50 ohm resistor.
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